The present invention relates to a cage for use in a roller bearing disposed, for example, on a crankpin of a crankshaft in an internal combustion engine and a method of making the same.
A roller bearing is typically disposed between a connecting rod and a crankpin of a crankshaft in an internal combustion engine. Such a roller bearing includes a cage and rollers retained the cage, but with no bearing rings. A cage for use in this type of roller bearing is made of metal since the ambient temperature is between 150.degree. and 160.degree..
The cage is disclosed, for example, in Japanese laid-open patent publication No. Sho 61-266827 (Prior art). Reference will briefly be made to FIGS. 5 and 6 showing an embodiment of the present invention. The construction disclosed in FIGS. 5, 6 and 7 is common to the prior art.
In the drawing figures, 1 is a cage for use in a roller bearing. 2 are rollers. 3 are pockets in which the rollers 2 are received, extending axially and spaced apart from one another circumferentially. 4 is an inner circumferential groove formed axially centrally of the cage 1 and having a predetermined width. 5 are partitions (stays) each provided between two adjacent pockets 3. Due to the formation of the inner circumferential groove 4, a central portion of each partition 5 in the axial direction of the cage is thinner than its remainder. Such a thin portion is designated by the reference numeral 6. Thick portions (side stays) are formed at opposite sides of the thin portion 6 and designated by the reference numeral 7.
Two outer projections 8 extend slightly from the outer surface of the thin portions 6 into the pocket 3. The distance between the two confronting outer projections 8 is less than the maximum diameter of the roller 2 so as to prevent the roller 2 from moving radially outwardly out of the pocket 3. Two grooves 9 are formed in the inner surface of the thick portions 7 and extend circumferentially of the cage. At open ends of the grooves 9, two inner projections 10 extend slightly from the inner surface the thick portions 7 into the pocket 3, respectively. Within the pocket 3, the distance between the confronting inner projections 10 is less than the maximum diameter of the roller 2 so as to prevent the roller 2 from moving radially inwardly out of the pocket 3. The groove 9 is formed by knurling, and the inner projections 10 are formed as a result of plasticdeformation in the process of such a knurling.
Each roller 2 is confined within the pocket 3 so as not to move radially inwardly and outwardly out of the pocket 3, but can be moved to a predetermined extend in both radial and circumferential directions. In use, the roller 2 is guided along the sides of the thick portions 7 of the cage 1.
Reference will briefly be made to a method of making the cage of this type.
Typically, a cylindrical pipe is, first, cut to a predetermined length. The piece thus cut is, then, recessed to provide an inner circumferential groove 4 (inner circumferential forming step). Thereafter, a suitable punch A is used to form several pockets 3 in the piece 3 (pocket forming step). The outer periphery of the piece is roughly abraded (rough abrasion step).
A portion of the cage 1 which surrounds the pocket 3 as shown particularly by a dot-dash-line in FIG. 7 is recessed due to pressure when the piece is punched in the pocket forming step. Thereafter, when such a portion is roughly and randomly abraded in a direction circumferentially of the cage, such a shear drop becomes more serious. Particularly the outer peripheral edges of the cage 1 at opposite sides of the pocket 3 become wavy or rugged as shown in FIG. 8.
In the event that the cage 1 serves to guide with its outer periphery, the top of each raised portion 11 of the wavy cage 1 is substantially in point contact with the inner peripheral surface of a connecting rod or outer ring. As a result, pressure increases at such a point of contact. Also, it is likely that an oil film formed at the inner peripheral surface of the outer ring is removed. This results in seizing of the components.
To this end, the inventor of the present invention has attempted to super finish the roller cage 1, just like the rollers, so as to substantially completely round the outer surface of the cage 1 and smoothen the rugged or wavy surface of the cage 1. Such a super finish is carried out in a manner shown in FIG. 9. The cage 1 is located between two confronting guide roller B and C. A grinding wheel D is used to apply a predetermined pressure to the outer periphery of the cage 1. While the cage 1 is being rotated by the two guide rollers B and C, the rugged surface of the cage 1 is abraded until the top of the rugged surface is flush with the bottom of a deepest recess 12.
A split-roller bearing is sometimes used between a connecting rod and a crankshaft. Such a split-roller bearing is formed by splitting the cage 1. If the split-cage has no rugged outer peripheral surface as stated earlier, lubricating oil may cause the split-cage to closely contact the inner peripheral surface of the connecting rod. This deteriorates movement of the connecting rod as the cage is rotated therewith. However, if the outer peripheral surface of the cage is not abraded and thus remains rugged, seizing occurs.
In view of the foregoing, it is an object of the present invention to provide a cage for a roller bearing which minimizes pressure between the outer peripheral surface of the cage and the inner peripheral surface of the outer ring so as to prevent seizing thereof, and an particular, to provide a split-cage which prevents the cage from sticking to the inner peripheral surface of the outer ring in order to ensure proper rotation.
It is another object of the present invention to provide a cage for a roller bearing which satisfies various and strict requirements.